1樓：
select distinct a1.a1,a1.a2,a2.b2 as 列1,
a3.c3 as 列2,
(a2.b2 + a3.c3) as 列3from a a1，
(select distinct b2 from b where a.a1=b.a1) a2,
(select distinct c2 from c where a.a1=c.a1) a3
這樣速度稍微快點，效率高點
2樓：獨駕舟千里去
select distinct a.a1,a.a2,(select distinct b2 from b where a.a1=b.a1) as 列1,
(select distinct c2 from c where a.a1=c.a1) as 列2,
((select distinct b2 from b where a.a1=b.a1)+(select distinct c2 from c where a.
a1=c.a1)) 列3
from a
只能這樣
sql起別名時不用as會加快效率嗎
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